Technical Abstract:
Barley (Hordeum vulgare L.) endosperm-specific (Bmy1) and ubiquitous (Bmy2) ß-amylase were studied during the late maturation phase of seed development in four genotypes. Sequencing of Bmy2 from genomic DNA revealed six polymorphisms in the introns and two synonymous SNPs in the coding region. Accumulation of Bmy2 mRNA was examined in developing seeds at 17, 19, and 21 days after anthesis (DAA). One genotype, PI 296897, had significantly higher Bmy2 RNA expression than the other three genotypes at all developmental stages. All four genotypes had Bmy2 mRNA levels decrease from 17 to 19 DAA, and remain the same from 19 to 21 DAA. Levels of Bmy1 mRNA were twenty thousand to over one-hundred thousand times more than Bmy2 mRNA levels in genotypes Legacy, Harrington, and Ashqelon at all developmental stages and PI 296897 at 19 and 21 DAA. PI 296897 had five thousand times more Bmy1 mRNA than Bmy2 mRNA at 17 DAA. However, Bmy2 protein was not found at 17 DAA in any genotype. The presence of Bmy2 was immunologically detected at 19 DAA and was present in greater amounts at 21 DAA. Importantly, Bmy2 protein was found in mature seeds and localized in the soluble fraction. Bmy1 protein was far more prevalent than Bmy2 at all developmental stages in all genotypes. Thus, the majority of ß-amylase activity in developing and mature seeds can be attributed to endosperm-specific ß-amylase. Additionally, the presence of the Bmy2 protein in mature seeds gives barley breeders a potential new target for malt quality improvement.